This project is a three part study of therapy for and diagnosis of microsporidiosis in patients with AIDS. Part A is a double-blind, placebo-controlled, multicenter study of albendazole for microsporidiosis. Part B is a compassionate use, open label study of albendazole that will enable us to treat patients who cannot be enrolled in Part A. Part C is a study of invasive and noninvasive techniques for the diagnosis of microsporidiosis.